K

K: informal abbreviation for thousand, used in expressions where the base unit is understood, such as "10K run" (10 kilometers) or "700K disk" (700 kilobytes or kibibytes). Note that "K" is also the symbol for the kelvin (see below). Also note that the symbol for the metric prefix kilo- (1000) is actually k-, not K-.
kappland: a traditional unit of land area in Sweden. The kappland is equal to 1/32 tunnland or 1750 square Stockholm feet (kvadratfot); this is equivalent to 154.26 square meters or about 184.50 sqaure yards.
karat (kt): a traditional measure of proportion, equal to 1/24, used by U.S. jewelers to express the purity of gold alloys. Thus "14-karat gold" is legally required to be at least 14/24, or 58.3%, gold. In Britain the unit is spelled carat, just like the weight unit for diamonds and other precious stones. American jewelers spell the unit of gold purity with the "k" and the weight unit with the "c" in order to distinguish more clearly between them.
katal (kat): a unit of catalytic activity, used especially in the chemistry of enzymes. A catalyst is a substance which initiates or facilitates a chemical reaction. Enzymes are proteins which act as catalysts within the bodies of living plants and animals. A catalyst has an activity of one katal if it enables a reaction to proceed at the rate of one mole per second. The unit is pronounced "cattle." The katal was officially added to the International System at the 21st General Conference of Weights and Measures in October 1999.
kati: a traditional Malaysian unit of weight, usually spelled catty in English.
kayser (K): a CGS unit used to measure light and other electromagnetic waves. The "wave number" in kaysers equals the number of wavelengths per centimeter. The unit honors J. H. G. Kayser (1853-1940), who compiled a giant atlas of chemical spectra. The unit is often abbreviated K, although this conflicts with the abbreviation for the kelvin.
keddah: a traditional Egyptian unit of liquid volume, also used in other parts of the Middle East. The keddah is equal to about 2.0625 liter (about 2.18 U.S. liquid quarts or 1.815 British imperial quarts).
keel: a British unit of weight used for measuring coal. After considerable variation, the keel of coal was standardized in 1695 as 21.2 long tons, or 47 488 pounds. This is the weight of coal which used to be carried by barges on the river Tyne in northern England; the barges were also called keels, from the Dutch word kiel for such a ship.
keg [1]: a traditional unit of volume or quantity, varying with the item contained in the keg. A keg of herring, for example, contains 60 fish. A keg of wine is frequently 12 U.S. gallons (about 45.42 liters), and a keg of beer is 15.5 U.S. gallons (about 58.67 liters).
keg [2]: a traditional unit of weight used to measure nails. A keg of nails weighs 100 pounds and thus has a mass of about 45.359 kilograms.
kelvin (K): the fundamental SI unit of temperature, previously called the degree Kelvin (°K) . One kelvin represents the same temperature difference as one degree Celsius. In 1967 the General Conference on Weights and Measures defined the temperature of the triple point of water (the temperature at which water exists simultaneously in the gaseous, liquid, and solid states) to be exactly 273.16 kelvins. Since this temperature is also equal to 0.01°C, the temperature in kelvins is always equal to 273.15 plus the temperature in degrees Celsius. The kelvin equals exactly 1.8 degrees Fahrenheit. The unit is named for the English mathematician and physicist William Thomson (1824-1907), later Baron Kelvin; he is remembered for his pioneering work on the physics of heat. See Temperature Converter.
ken: a traditional Japanese unit of length comparable to the English fathom. The ken equals 6 shaku, which is about 1.818 meters (5.965 feet). The ken is the length of a traditional tatami mat.
kerat: a traditional Middle Eastern unit of length, equal to about 9/8 inch or 2.86 centimeters. The unit has the same Arabic root as the carat.
key: slang for kilo, meaning kilogram.
kibi- (Ki-): a binary prefix meaning 2¹⁰ = 1024. This prefix, adopted by the International Electrotechnical Commission in 1998, replaces kilo- for binary applications in computer science. Thus 1024 bytes of storage is officially a kibibyte, not a kilobyte. The prefix is a contraction of "kilobinary."
kilderkin: an old British unit of volume equal to 1/2 barrel. Based on the current British barrel, this would be 18 (imperial) gallons, which is about 2.9 cubic feet or 78 liters. Older kilderkins were generally in the range of 16-18 gallons. The word comes from a Dutch word for a small cask.
kilo: an informal name for a kilogram.
kilo- (k-) [1]: a metric prefix meaning 1000. The prefix is a modification of chilioi, the Greek word for a thousand. See Prefix
kilo- (k-) [2]: in measuring the memory of a computer, the prefix kilo- often means 2¹⁰ = 1024 instead of 1000. By a 1998 resolution of the International Electrotechnical Commission, the new prefix kibi- (Ki-) should replace kilo- for 2¹⁰. However, this doesn't seem to be happening.
kiloampere (kA): a unit of electric current equal to 1000 amperes.
kilobar (kbar or kb): a metric unit of pressure, used particularly in industrial applications and in geology for measuring high pressures. The kilobar equals 1000 bars, 100 mega pascals, or about 14 503 pounds per square inch. (Note: in the investment world a kilobar is not a unit; it is a 1 kg bar of gold, silver, or platinum.)
kilobase (kb): a unit of genetic information equal to the information carried by 1000 pairs of the base units in the double-helix of DNA; also used as a unit of relative distance equal to the length of a strand of DNA containing 1000 base pairs.
kilobecquerel (kBq): a unit of radioactivity equal to 1000 atomic disintegrations per second or 27.027 nanocuries (nCi).
kilobit (kbit or kb): a unit of information equal to 1024 bits or 128 bytes, now supposed to be called a kibibit.
kilobyte (kB): a unit of information equal to 1000 bytes. As a unit of computer storage the kilobyte is usually equal to 1024 bytes, although this should now be called a kibibyte.
kilocalorie (kcal): an ambiguous metric unit of energy. The ambiguity arises because there are two "calories" in common use, identified in this dictionary as the calorie (the small or gram calorie equal to 4.1868 kilojoules) and the Calorie (the large or kilogram calorie equal to 4.1868 megajoules). The term kilocalorie usually means 1000 calories, which is the same as 1 Calorie. In other words, "kilocalorie" is generally used as short form of "kilogram calorie."
kilocurie (kCi): a unit of radioactivity equal to 1000 curies or 37 terabecquerels (TBq), that is, 37 trillion atomic disintegrations per second. The strength of the powerful radiation sources used in cancer therapy are customarily stated in kilocuries.
kilocycle (kc): 1000 cycles; a term sometimes used as an informal name for the kilohertz.
kilogauss (kGs): a metric unit of magnetic flux density equal to 1000 gauss or 0.1 tesla. The strength of industrial magnets and solenoids is often expressed in kilogauss, although this unit is being gradually replaced by the tesla.
kilogram (kg): the fundamental unit of mass in the SI and MKS versions of the metric system. The kilogram is defined as the mass of the standard kilogram, a platinum-iridium bar in the custody of the International Bureau of Weights and Measures (BIPM) near Paris, France. Copies of this bar are kept by the standards agencies of all the major industrial nations, including the U.S. National Institute of Standards and Technology (NIST). One kilogram equals exactly 1000 grams, or about 2.204 622 6 pounds.
kilogram mole, kilogram molecule, kilogram molecular weight (kgmol or kgmole): various older names for a unit of the amount of a chemical compound. One kilogram mole of a compound is the number of kilograms of the compound equal to the molecular weight of a molecule of that compound measured in atomic mass units. The correct name for this unit is the kilomole (kmol).
kilogram of force (kgf): a unit of force equal to the gravitational force on a mass of one kilogram. One kilogram of force equals 9.806 65 newtons, or 2.204 622 6 pounds of force in the traditional English system. Using this unit revives the old confusion between mass and weight, one of the worst features of traditional measurement systems, so it is really a very bad idea. However, kilograms of force have been used rather frequently in engineering and physics.
kilohertz (kHz): a common unit of frequency equal to 1000 per second.
kilojoule (kJ): a common metric unit of work or energy, comparable to the British thermal unit (Btu). In fact, one kilojoule equals approximately 0.947 817 Btu. In other energy units, the kilojoule is also equivalent to 0.238 846 kilocalories, 0.277 778 watt hour, or 737.562 foot-pounds in the traditional English system.
kiloline: a metric unit of magnetic flux, equal to 1000 lines [2] or 10 microwebers.
kiloliter (kl or kL): a metric unit of volume. The kiloliter is identical to the cubic meter: it equals about 35.3147 ft³, 1.307 95 yd³, 264.17 U.S. gallons, 219.99 British Imperial gallons, 7.497 U.S. bushels, or 6.049 British imperial bushels.
kilomega- (kM-): an obsolete metric prefix denoting 10⁹ (1 U.S. billion). This prefix has been replaced by giga- (G-).
kilometer (km): a common metric unit of length or distance. One kilometer equals exactly 1000 meters, about 0.621 371 19 mile, 1093.6133 yards, or 3280.8399 feet. Oddly, higher multiples of the meter are rarely used; even the distances to the farthest galaxies are usually measured in kilometers. The unit is sometimes pronounced with the accent on the first syllable and sometimes on the second. Both are acceptable; there are no official pronunciations for SI units. See Length
kilometer per hour (km/h): a common metric unit of speed or velocity. 1 km/h is equal to 5/18 meter per second, 0.621 371 19 mi/hr or 0.911 344 42 ft/sec.
kilonewton (kN): a common metric unit of force, the kilonewton equals 1000 newtons; it is a force that will accelerate a mass of 1 metric ton at the rate of 1 meter per second per second. One kilonewton equals 101.972 kilograms of force, 224.809 pounds of force or 7233.01 poundals.
kilohm: a unit of electric resistance equal to 1000 ohms.
kilo-oersted (kOe): a CGS unit of magnetic field strength equivalent in MKS units to 79 577.472 ampere-turns per meter. The unit, used for stating the field strengths of industrial magnets, is almost always spelled with the hyphen.
kiloparsec (kpc): a unit of distance used in astronomy, the kiloparsec equals 1000 parsecs, 3261.631 light years, 3.085 678 x 10¹⁶ kilometers, or about 19.18 quadrillion miles. The Solar System is located about 8 kiloparsecs from the center of the Milky Way galaxy.
kilopascal (kPa): a common metric unit of pressure. One kilopascal equals 1000 pascals (Pa), 10 millibars(mb), or about 0.145 038 pounds per square inch (lbf/in² or psi), 20.8855 pounds per square foot, 7.502 millimeters of mercury (mm Hg), 0.2953 inches of mercury (in Hg), 4.015 inches of water column (in WC), or 0.3346 foot of head (ft hd).
kilopond (kp): another name for the kilogram of force (kgf) (see above).
kilorad (krad): a common unit of radiation dose equal to 1000 rads, 10 grays, or 10 joules of energy per kilogram of mass.
kiloton (kt or kton) [1]: an ambiguous unit of mass, ambiguous because it may refer to 1000 U.S. tons (907 185 kilograms), 1000 British tons (1 016 047 kilograms), or 1000 metric tons (1 million kilograms). To avoid this confusion, the metric unit should be written kilotonne.
kiloton (kton) [2]: a unit of explosive energy equal to the energy released by exploding 1000 U.S. tons (2 million pounds) of TNT. This is about 4.18 terajoules (4.18 x 10¹²joules) or 4 billion Btu.
kilovolt (kV): a common unit of electric potential equal to 1000 volts. Electric distribution lines operate at potentials of anywhere from several to several hundred kilovolts.
kilovolt ampere (kV·A): a common unit of load in power engineering, equal to 1000 volt amperes.
kilowatt (kW): a common metric unit of power, equivalent to 1000 watts, about 1.341 022 horsepower, or 737.562 foot-pounds per second.
kilowatt hour (kW·h or kw hr): the commercial unit of electric energy. One kilowatt hour represents the amount of energy delivered a rate of 1000 watts over a period of one hour. Since the watt is 1 joule/sec and there are 3600 seconds in an hour, the kilowatt hour is equivalent to exactly 3.6 megajoules of energy, or about 3412.141 Btu, 859.846 (kilogram) Calories, or about 2.655 million foot pounds.
kin: the Japanese version of the catty, a common weight unit of the Far East. The Japanese identified this unit with a traditional unit equal to about 1.323 pounds or almost exactly 600 grams; this is about 0.75% smaller than the Chinese catty.
kip [1]: an informal unit of mass, sometimes used by engineers to express the amount of load on a structure. One kip equals 1000 pounds (453.59 kilograms). The name of the unit is an abbreviation of "kilopound."
kip [2]: an informal unit of force equal to 1000 pounds of force or about 4.4482 kilo newtons.
kip [3]: an old English word for a bundle of hides. It was sometimes used as a unit of quantity, usually equal to 50.
klafter [1]: a traditional unit of distance in German-speaking countries, comparable to the English fathom. The Austrian klafter is equal to 1.8965 meters (6.22 feet). In Switzerland the klafter was brought into the metric system at exactly 1.8 meters (5.9055 feet). This unit is also called the faden.
klafter [2]: a traditional German unit of volume for stacked firewood, comparable to the English cord. A klafter of wood was generally 1 klafter tall and 1 klafter long, but there was less agreement on its width, that is, the length of the logs. A common width was 3 fuss or 0.5 klafter, making the volume about 3.41 steres (cubic meters) or 0.941 cord by the Viennese definition, 3.34 steres or 0.921 cord in northern Germany.
klick, klik: see click.
Knoop hardness (HK or KHN): a measure of the hardness of a metal introduced by Knoop in 1939. The Knoop test is similar to the Vickers test in that a diamond penetrator is used to indent the sample being tested, but it uses a rhombohedral diamond rather than a pyramidal diamond point. It is similar to the Rockwell test in that the hardness measure is the depth of the penetration rather than its area. The result is measured in kilograms of force per square millimeter but should be stated as an empirical measurement, without units.
knot (kn or kt): a unit of velocity equal to one nautical mile per hour. Knots are customarily used to express speeds at sea, including the speed of the ship as well as the speeds of the wind and of the current. The word comes from the former method of measuring a ship's speed, which involved use of a knotted cord called the log line. One knot equals about 1.1508 miles per hour, exactly 1.852 kilometers per hour, or 0.5143 meters per second. The knot has also been used incorrectly as a name for the nautical mile. See Speed
köddi: a traditional Arabic unit of volume, equal to about 4/3 British imperial gallon or 7.58 liters.
koku: a traditional Japanese unit of volume, equal to about 180.391 liters (39.68 British imperial gallons or 6.37 cubic feet). The unit originated as an estimate of the amount of rice needed to feed a person for a year.
kommerzlast: German for "commercial load," now interpreted as a metric unit equal to exactly 3 tonnes (about 6613.9 pounds).
kon: Korean name for the catty.
koyan: a Far Eastern unit of weight equal to 4000 catty or 5333.33 pounds (8/3 short ton).
kph: an abbreviation for kilometers per hour. This abbreviation should not be used; the correct symbol is km/h.
krina: a traditional unit of volume in Bulgaria, now expressed in the metric system as being equal to exactly 20 liters (4.40 British imperial gallons or 5.28 U.S. liquid gallons).
ksf, ksi: symbol for kips (kilopounds) per square foot or per square inch, traditional engineering units of pressure or stress. 1 ksf = 47.880 257 kilo pascals (kPa) and 1 ksi = 6.894757 megapascals. See Force
kulmet: a traditional Latvian unit of volume equal to about 10.93 liters (2.40 British imperial gallons or 2.89 U.S. liquid gallons). A similar Estonian unit, the külimet, equals about 11.48 liters (2.53 British imperial gallons or 3.03 U.S. liquid gallons).
kunitz or Kunitz unit: a unit used in biochemistry to describe the concentration or activity of the enzyme ribonuclease, which attacks ribonucleic acid (RNA). Ordinarily RNA absorbs ultraviolet light, so the activity of ribonuclease can be measured by observing the decrease of this absorption. One kunitz is the concentration of the enzyme causing a decrease of 100% in the absorption in a time of one minute, the measurement being made under certain standard laboratory conditions. The unit's name recognizes the Russian-American biochemist M. Kunitz, who proposed the standard test in 1946.
kvadrat-: Scandinavian prefix meaning "square." In particular, a kvadratmeter is a square meter. The prefix is common to Danish, Norwegian, and Swedish.
kwan: a traditional Japanese unit of weight equal to 6.25 kin (see above), which is about 8.27 pounds or 3.75 kilograms.
kyu: a metric unit of distance used in typography and graphic design. The kyu, originally written Q, is equal to exactly 0.25 millimeter or about 0.71 point [2]. The spelling "kyu" seems to have been introduced by the software company Macromedia.